I couldn't bind mouse buttons during the beta for the life of me. I've had no issues since it was released though. What kind of mouse do you have out of curiosity?

A Logitech G500.

And when I press assign key in the mouse column, the "press key" dialog comes up but it doesn't read my mouse button press to assign it. For example, I usually have my knife set to button 4 and grenade to button 5, but it doesn't read it when I press the button.